This invention broadly relates to a method and an apparatus for collecting matter floating on a body of water, namely collecting such matter by skimming a surface layer carrying the matter to be collected and separating the matter from the water of the skimmed layer. Certain embodiments of the invention are specially directed to the collection of spilled oil, particularly low-viscosity oil. The invention will therefore be described with emphasis on that application, but it is also applicable to other types of floating debris.
According to a known skimming technique, a collection vessel is immersed in the body of water carrying the matter to be collected such that an overflow rim of the collection vessel is just beneath the surface. Water is constantly pumped out of the lower portion of the collection vessel at such a rate that the outflow from the collection vessel balances the inflow of water into the collection vessel over the rim thereof to maintain a sink--that is, an area the level of which is lower than the level of the surrounding water--in the collection vessel. The floating matter carried or entrained by the inflowing water is accumulated in the sink and can be removed continuously or intermittently. Examples of this skimming technique are disclosed in DE-B-20 30 209 and WO97/07292 (published Feb. 27, 1997).
This technique lends itself to a rapid and energy-efficient collection of oil or other debris floating on water, because large volumes of water can be rapidly pumped through the collection vessel at a fairly low rate of energy consumption.
Spillage of low-viscosity oil in waterways and other open waters occurs frequently and presents special problems. When an oil spillage is detected, it is desirable to be able quickly to take a sample of the oil so that it can be analyzed. However, low-viscosity oil forms an extremely thin layer on the water surface, and even with a very high rate of flow of water through the collection vessel it is very difficult, or even almost impossible, to collect substantial amounts of the oil using known techniques. Actually, it is hardly possible to collect even an amount of oil which is sufficient for an analysis of the characteristics of the oil.